1. Field of the Invention
The present invention relates to a crankshaft supporting structure for a horizontally opposed type internal combustion engine used for automobiles, motorcycles, airplanes and the like. In particular, the present invention relates to a crankshaft supporting structure for supporting a journal at an intermediate portion of a crankshaft in a horizontally opposed type internal combustion engine. The engine includes a crankshaft and pluralities of first and second pistons connected to the crankshaft. The pluralities of first and second pistons are disposed opposite to each other with the crankshaft therebetween, and are arranged with an offset from each other along the axial direction of the crankshaft. Furthermore, the engine includes a crankcase for containing and supporting the crankshaft, and first and second cylinder blocks connected to and disposed on opposite sides of the crankcase and having cylinder bores for slidably receiving the pluralities of first and second pistons therein. The crankcase is split along a plane containing the axis of the crankshaft into first and second case halves connected respectively with the first and second cylinder blocks.
2. Description of Background Art
A structure for supporting a middle journal of a crankshaft in a horizontally opposed type internal combustion engine as described above is known. First, Japanese Patent Laid-open No. 2000-110582 discloses a structure, wherein a first case half is provided integrally with a journal supporting wall for supporting a half periphery portion of a middle journal of a crankshaft. In addition, a bearing cap for supporting the other half periphery portion of the journal is bolt-connected to the journal supporting wall. Second, a structure is known, wherein first and second case halves are provided integrally with first and second journal supporting walls for respectively supporting half periphery portions of a middle journal. The first and second journal supporting walls are bolt-connected at outside portions thereof.
However, in the first structure above, the bearing cap is required to connect to the first case half. Accordingly, the number of component parts is increased. Furthermore, the second case half cannot contribute greatly to reinforcement of the support for the crankshaft. On the other hand, in the second structure above, the distance from the middle journal of the crankshaft to the bolt connection portions of the case halves is required to be large. Accordingly, not only the journal supporting wall but also portions of the crankcase must be increased in thickness for the purpose of obtaining sufficient support rigidity for the crankshaft. This results in an increase in the weight of the internal combustion engine.
The present invention has been made in consideration of the above-mentioned points. Accordingly, an object of the present invention is to provide a crankshaft supporting structure for a horizontally opposed type internal combustion engine which utilizes the first and second case halves of the crankcase to rigidly support the middle journal of the crankshaft. With this structure, a simplification in structure and a reduction in weight are accomplished.
In order to attain the above object, a horizontal opposed type internal combustion engine includes a crankshaft and pluralities of first and second pistons connected to the crankshaft, disposed opposite to each other with the crankshaft therebetween and arranged with an offset from each other along the axial direction of the crankshaft. A crankcase is included for containing and supporting the crankshaft, and first and second cylinder blocks are connected to and disposed on opposite sides of the crankcase and have cylinder bores for slidably receiving the first and second pluralities pistons. The crankcase is split along a plane containing the axis line of the crankshaft into first and second case halves connected respectively with the first and second cylinder blocks. The first and second case halves are integrally provided with first and second journal supporting walls rotatably supporting a middle journal of the crankshaft therebetween. The first and second journal supporting walls front the cylinder bores of the first and second cylinder blocks, and the first and second journal supporting walls are connected by a plurality of first bolts inserted from the side of the cylinder bore of the first cylinder block and disposed on opposite sides of and in proximity to the middle journal.
According to the first characteristic feature, the first and second journal supporting walls for supporting therebetween the middle journal of the crankshaft can easily be bolt-connected, without being interfered with by the first and second cylinder blocks.
In addition, since the journal supporting walls are bolt-connected on both sides of and in proximity to the middle journal of the crankshaft, rigidity of support for the middle journal of the crankshaft can be enhanced effectively. As a result, the crankcase can be reduced in wall thickness, leading to a reduction in weight.
In addition, the bearing cap for supporting the crankshaft is unnecessary. Accordingly, it is possible to obtain a reduction in the number of component parts and a simplification in structure.
In addition to the first characteristic feature, the present invention also includes the first and second journal supporting walls connected by a plurality of second bolts inserted from the side of the cylinder bore of the second cylinder block and arranged on opposite sides of and in proximity to the middle journal.
According to the second characteristic feature, even though the amount of exposure of the first and second supporting walls into the cylinder bores of the first and second cylinder blocks is small and the bolts to be used are small in diameter, the journal supporting walls can be connected by at least four bolts inserted from the first and second cylinder blocks. As a result, the journal supporting walls can be provided with sufficient binding force.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.